The successful operation of avalanche photodetector (APD) focal plane arrays is largely dependent upon all pixels producing sufficiently low current under no illumination. The necessary complexity of the read-out integrated circuit (ROIC) chips, which are typically flip-chip bonded to APD photodetector arrays (PDAs), places a premium on ROIC pixel real estate relative to that of ROICs used with conventional PDA technologies. This hinders individual pixel addressability and, in fact, APD PDAs are biased in parallel. Consequently, when individual pixels exhibit abnormally low impedance relative to their neighbors, these “leaky” pixels effectively short-circuit the entire FPA, preventing operation of the device.
The present state of materials processing technology is sufficient to produce working APD PDAs, but point defects leading to catastrophically leaky pixels remain frequent enough to limit device yield.